The invention relates to a method for checking the centering of spectacles worn by a spectacle wearer.
The invention furthermore relates to an apparatus for checking spectacles worn by a spectacle wearer.
When a spectacle wearer purchases spectacles with optically effective spectacle lenses, faulty workmanship may occur during the production of the spectacles. By way of example, the left and right spectacle lenses may have been mixed up, or one or both spectacle lenses may have the wrong refractive power. Furthermore, the spectacle lenses may be wrongly centered.
While the first-mentioned faults can be identified relatively easily by measuring the spectacle lenses and comparing them to the prescription, it requires more effort to identify a wrong centering of the spectacle lenses.
These days, progressive lenses have a far reference point and a near reference point, which are determined for each progressive lens during production. These points cannot be identified on the spectacle lens. Furthermore, progressive lenses are provided with permanent markings, which are usually engraved by laser and just about visible to the unaided eye. The permanent markings are arranged on the spectacle lens at a predetermined relative position with respect to the far reference point and the near reference point and possibly also contain information relating to the specific spectacle lens.
When a spectacle wearer purchases spectacles, the spectacle lenses must be centered in the frame in relation to the individual pupil spacing and possibly also to the position of the corneal vertex of the spectacle wearer so that the spectacle lenses are correctly positioned in this frame in optical terms.
By way of example, this can be brought about by means of a video centering instrument, wherein the spectacle wearer puts on the desired frame and the position of the pupils of the spectacle wearer and the fit and shape of the frame are then registered by means of a frontal and a lateral camera. Such a video centering instrument is distributed by the applicant under the name “Video Infral RVT”. The optimum position of the spectacle lenses in the frame is then calculated from the measured values, and the spectacle lenses are edged accordingly and inserted into the frame.
If no video centering instrument is available, the desired frame with optically neutral support discs are put onto the spectacle wearer by the optician and the latter manually marks the position of the centering points on the support discs relative to the position of the pupils. The optician can then use templates, provided to the optician by the spectacle-lens producers, to convert the manually applied markings into correct positioning of the spectacle lenses.
If there now is a wrong centering of the finished spectacles and the spectacle wearer lodges a complaint with his/her optician, then only manual procedures have been used to date for determining a possible centering error.
The optician firstly looks for the permanent markings on the spectacle lenses and marks them using a colored pen so they can be identified more easily. Then the aforementioned templates are used to draw on the far reference point and the near reference point, the spectacles are put on the spectacle wearer and checking takes place as to whether the actual reference points correspond to the drawn-on nominal reference points. To this end, use can be made of what is known as Victorin's method.
It is clear that this procedure is very cumbersome and is in turn inflicted with a risk of error. An additional difficulty in the case of modern spectacle lenses, which are provided with a dirt-repellent coating on the basis of the lotus effect, is that markings cannot be applied at all using the conventional colored pens.
DE 103 33 426 A1 discloses an apparatus by means of which permanent markings can be identified on spectacle lenses and the position of which permanent markings can be determined on the spectacle lens.
DE 10 2006 033 491 A1 discloses a centering instrument wherein engraving points are also determined, but only in the context of manual marking of saddle points.